Comparison of Beef Cattle Grazing Management Practices and their Effects on Runoff Water Quality in Louisiana

Abstract

Management-intensive grazing (MIG) allows better use of grazed forage crops with short-duration grazing in small paddocks and with this study; the water quality was compared for two grazing management methods. Year-round grazing with MIG and continuous stocking (CS) were compared. Four 0.81-ha plots for two replications of the grazing systems were established. Twenty 0.04 ha (0.1 ac) paddocks, established with power fencing, allowed daily cattle rotation in MIG system. Continuous grazing and MIG used the same stocking rate on each experimental plot (0.81 ha). Each year, two crossbredbeef (Bos taurus) heifers (390 kg ± 12 kg; 12-14 mo at start) were maintained on each plot year-around for 3 yr, with additional yearling heifers added to maintain similarforage availability between stocking methods. Common bermudagrass (Cynodon dactylon [L] Pers.) was grazed in summer and annual ryegrass (Lolium multiflorum Lam.) was over-seeded into the sod during October for winter and spring grazing. Forage mass was determined monthly and available forage dry matter (DM) was maintained at approximately 1120 kg DM ha-1 Runoff water samples were collected during 42 rainfall events from May 2001 through March 2004. No significant treatment differences (P > 0.10) were found in most of the water quality parameters. Runoff as a percentage of the 3-yr average annual rainfall of 1869 mm was 34% for MIG and 42% CS. The average flow-weightedconcentrations of soluble reactive phosphorus (SRP) varied from 5.08 mg P L–1 (ppm) to 8.22 mg P L–1 (ppm) while the NH+4–N ranged from 1.07 mg N L–1 (ppm) in year one to 10.11 mg N L–1 (ppm) for the second year (P < 0.05) for year effect. Total annual average forage production was greater (P < 0.05) in the MIG compared to CS with19,796 kg ha-1 for MIG vs. 16,964 kg ha-1 for CS. Beef production also increased with the MIG system with an annual total beef gain from MIG at 422 kg ha-1 y-1 vs. CS at 330 kg ha-1 yr-1.